1. Field of the Invention
This invention relates to a synchronizer for transmissions.
2. Description of the Prior Art
In general, a manual transmission for an automobile employs a synchronizer for effecting a speed changing operation easily and speedily. This synchronizer is provided between intermeshing splines formed on a gear in a synchronized unit and a sleeve connected to a synchronizing unit.
An example of a 3-cone type synchronizer made according to the conventional techniques and used in a gear transmission will roughly be described with reference to FIGS. 3 and 4. FIG. 3 is a sectional view of a conventional 3-cone type synchronizer 30 in a gear transmission, and FIG. 4 a sectional view taken along the line IV--IV in FIG. 3. The line III--III in FIG. 4 is the line along which FIG. 3 is taken. A sleeve 1 and a clutch hub 2 are joined to each other slidably via their respective splines 3, 4. The sleeve 1, clutch hub 2 and a block ring 5 are fixed in the rotational direction by an insert key 13, and the claws 14 of the inside ring 7 extend into the recesses in the block ring 5. Accordingly, the sleeve 1, clutch hub 2, block ring 5 and inside ring 7 are fixed with respect to one another in the rotational direction and adapted to rotate at the same number of revolutions per unit time. A first gear 11 or a second gear 12 is spline-connected to a synchromesh cone 18 via splines 21, 29. The synchromesh cone 18 is provided with a plurality of circumferentially-extending cross-sectionally rectangular recesses 27, and the outside ring 6 with a plurality of circumferentially-extending locking claws 24. The synchrocone 18 and outside ring 6 are fixed to each other in the rotational direction by the locking claws 24 engaged with the recesses 27, in such a manner that the synchromesh cone 18 and outside ring 6 are rotated at the same number of revolutions per unit time. The outer tapering surface, i.e. a conical surface 16 of the outside ring 6 contacts the inner tapering surface, i.e. a conical surface of the block ring 5, and the inner tapering surface, i.e. a conical surface 15 of the outside ring 6 the outer tappering surface, i.e. a conical surface 32 of an inside ring 7. When a shifting action of the transmission is carried out, the phases of the sleeve 1 and block ring 5 are matched by the insert key 13, and a dog tooth 35 of the sleeve 1 presses that 34 of the block ring 5 to start a synchronizing operation. This synchronizer has three conical surfaces, i.e. tapering surfaces which have the number of a relative revolution. To be concrete, they are the contact surface 31 of the outer tapering surface 31 of the outside ring 6 and inner tapering surface 16 of the block ring 5, contact surface 32 of the inner tapering surface 32 of the outside ring 6 and outer tapering surface 15 of the inside ring 7, and contact surface 33 of the inner tapering surface of the inside ring 7 and outer tapering surface of the synchrocone 18. Reference numeral 9 in the drawing denotes key springs.
The above-described 3-cone type synchronizer 30 in a transmission has three conical surfaces, i.e. three mutually contacting tapering surfaces, and there is a limit to the accuracy of each tapering surface, so that the play, i.e. inclination of the block ring 5 with respect to the synchromesh cone 18 increases. Consequently, it becomes difficult to generate a stable cone torque when the synchronizer is operated. In order to connect three members, in other words, in order to connect the block ring 5, outside ring 6, inside ring 7 and synchrocone 18 together properly, it is necessary that these members be formed so as to provide suitable clearances between these members and between the locking claws and recesses. Due to these clearances, play in the rotational direction occurs between these members. Moreover, the generation of cone torque tends to delay due to the limited accuracy of the conical surfaces. The condition of engagement of the locking claws 24 of the outside ring 6 with the synchromesh cone 18 is as shown in FIG. 4. Namely, while the outside ring 6 and synchromesh cone 18 are rotated relatively to each other, a leading end portion 28 of a locking claw 24 and a circumferentially inner surface 26 of a recess 27 in the synchromesh cone 18 are engaged with each other. Consequently, the inclination of the outside ring 6 is prevented, and the outside ring 6 comes near the block ring 5, so that the locking claw 24 and synchromesh cone 18 contact each other reliably. However, since no axial thrust works on the locking claw 24 of the outside ring 6, a clearance 20 is left between the outside ring 6 and clutch hub 2. Therefore, the outside ring 6 is readily inclined when a shifting operation is carried out.
Japanese Patent Publication No. 17642/1971 (U. S. Pat. No. 3,414,098) discloses a synchronizer structure shown in FIG. 5. In this synchronizer structure 50, a ring 59 is provided between a gear 53 and a clutch drum 58, and has clutch surfaces 60, 61 engageable with clutch surfaces 56, 67. A clutch drum 58 is provided with teeth 62 which are drive-engaged reliably with a clutch sleeve 54 when the clutch sleeve 54 is displaced axially. The clutch drum 58 is drive-engaged reliably with the clutch sleeve 54 and gear 53. The ring 59 has a plurality of projecting portions 63, and a torque transmission hub 51 a plurality of radially-extending recesses 64, the projecting portions 63 being engaged with the recesses 64 to attain the driving engagement of the ring 59 with the torque transmission hub 51. This synchronizer structure 50 is operated as follows. When the clutch sleeve 54 is displaced axially, a synchronizer ring 52 and ring 59 frictionally engage the clutch surfaces 55, 56 of the clutch drum 58 to enable the gear 53 and torque transmission hub 51 to be reliably drive-engaged. This synchronizer structure 50 also has problems similar to those with the above-described 3-cone type synchronizer. Namely, although the recesses 64 in the torque transmission hub 51 and the projecting portions 63 of the ring 59 are engaged, thrust causing the ring 59 to impinge upon the torque transmission hub 51 does not occur. Therefore, it is clear that the construction of the synchronizer structure is incapable of preventing the synchronizer ring 52 and clutch drum 58 from being inclined when a shifting operation is carried out.